Eclipse Thiele/Small, difficult to find!

If you're entering parameters into a design program, Vd will be auto-calculated if you have some other parameters entered.  Try this:  in the blank driver editor box, enter the values Xmax and Sd.  You will see two calculated values appear:  Dd and Vd.

Here an example of a database I filled in the other day.  The values in green are entered by me, the values in blue were calculated by WinISD:  autocalc.jpg

If you're looking for volume displacement of the whole driver installed for the purpose of calculating airspace, the value Vd will not give you what you want.  In the example above, the actual displacement of the sub, front-mounted to a 3/4" baffle, was listed as .07 cu ft...where in the pic you can see that the value of Vd is only .045 ft^3.  This is something I do a lot of guesswork on;  comparing given displacements for several subs and making a call for a particular one I don't have info on.  And, if you are doubling the baffle face, the displacement would be less by the cu. inches of the extra cutout hole.

Yes, that may be why.  Here's what I found for the 9122.  It may not be 100% accurate but it should be close enough for modeling work.

Fs=27Hz; Qts=0.30; Re=3.8; Vas=90.6 liters; Xmax = 3.81 cm (one way); Sd=335 cm^2